Semiconductor devices are abundant today in different forms of electronic and optical systems. Current research and development trends are pushing the data rates of computer semiconductor chips to speeds well in excess of 1 Gigahertz and optical semiconductor laser diodes are being pushed to ever increasing output powers. Many other examples could be cited with similar trends, faster speeds and higher output powers. Semiconductor chips can generate sufficient internal heat to degrade their operational performance and in extreme cases may cause permanent damage to the chip. Typically, these considerations lead to restrictions on the ambient temperature ranges the devices can operate over and limitations on how the devices can be packaged. Given this, techniques have been developed to assist in cooling these devices to increase their operational range and performance. Some semiconductor chips are mounted on active devices such as thermo-electric (TE) coolers, sometimes referred to as Peltier coolers or heat pumps, which are electrically driven and actively remove heat from semiconductor devices. Typically, in the case of laser diodes, the semiconductor chip is metallized on its bottom surface and adhered to a submount, which in turn is mounted via soldering to the TE cooler. In turn, the TE cooler is typically mounted on a physically larger heat sink which dissipates thermal energy received from TE cooler.
Laser diodes have high demands for heat removal from semiconductor devices. This is because the thermal energy is generated in extremely small volumes, the active lasing region may be as small as one micron or so in the cross sectional dimension extending over a length on the order of a millimeter. Given this, the thermal energy density is extremely high and it is important to remove the heat from this region efficiently. In current manufacturing techniques, these devices are fabricated by growing the semiconductor layers on a substrate material via an epitaxial process such as molecular beam epitaxial (MBE) growth or metal organic chemical vapor deposition (MOCVD). To maintain mechanical strength and integrity during the manufacturing process, the substrate material during the growth process may be thicker than in the final product. The substrate material is mechanically ground and polished to its final thickness dimension following the growth process. This is done for two reasons.
First, hundreds, maybe even thousands, of these identical semiconductor devices are fabricated on a common substrate wafer which will need to be mechanically cut (cleaved) and separated from one another. Secondly, if the substrate material were left in its thick format the devices would be in danger of overheating and self-destructing due to the large thermal impedance across the substrate. Given this, the substrate material may be mechanically lap polished prior to cleaving. Unfortunately, some popular semiconductor materials (e.g., Indium Phosphide) are extremely brittle and are prone to shattering during the mechanical lapping process.
In view of these problems, there is a need for an improved method for enhancing the removal of heat from semiconductor devices, particularly laser diodes. There is also a need to reduce breakage of semiconductor chips in the final mechanical lapping step of fabrication.